Method of thermal processing structures formed on a substrate

ABSTRACT

The present invention generally describes one ore more methods that are used to perform an annealing process on desired regions of a substrate. In one embodiment, an amount of energy is delivered to the surface of the substrate to preferentially melt certain desired regions of the substrate to remove unwanted damage created from prior processing steps (e.g., crystal damage from implant processes), more evenly distribute dopants in various regions of the substrate, and/or activate various regions of the substrate. The preferential melting processes will allow more uniform distribution of the dopants in the melted region, due to the increased diffusion rate and solubility of the dopant atoms in the molten region of the substrate. The creation of a melted region thus allows: 1) the dopant atoms to redistribute more uniformly, 2) defects created in prior processing steps to be removed, and 3) regions that have hyper-abrupt dopant concentrations to be formed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 11/459,856 (APPM/005635.03), filed Jul. 25, 2006, which claimsbenefit U.S. Provisional Patent Application Ser. No. 60/780,745(APPM/005635L), filed Mar. 8, 2006, which are herein incorporated byreference.

This application is related to U.S. patent application Ser. No.11/459,847 (APPM/005635), filed Jul. 25, 2006, and to U.S. patentapplication Ser. No. 11/459,852 (APPM/005635.02) filed Jul. 25, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention generally relate to a method ofmanufacturing a semiconductor device. More particularly, the inventionis directed to a method of thermally processing a substrate.

2. Description of the Related Art

The integrated circuit (IC) market is continually demanding greatermemory capacity, faster switching speeds, and smaller feature sizes. Oneof the major steps the industry has taken to address these demands is tochange from batch processing silicon wafers in large furnaces to singlewafer processing in a small chamber.

During such single wafer processing the wafer is typically heated tohigh temperatures so that various chemical and physical reactions cantake place in multiple IC devices defined in the wafer. Of particularinterest, favorable electrical performance of the IC devices requiresimplanted regions to be annealed. Annealing recreates a more crystallinestructure from regions of the wafer that were previously made amorphous,and activates dopants by incorporating their atoms into the crystallinelattice of the substrate, or wafer. Thermal processes, such asannealing, require providing a relatively large amount of thermal energyto the wafer in a short amount of time, and thereafter rapidly coolingthe wafer to terminate the thermal process. Examples of thermalprocesses currently in use include Rapid Thermal Processing (RTP) andimpulse (spike) annealing. While such processes are widely used, currenttechnology is not ideal. It tends to ramp the temperature of the wafertoo slowly and expose the wafer to elevated temperatures for too long.These problems become more severe with increasing wafer sizes,increasing switching speeds, and/or decreasing feature sizes.

In general, these thermal processes heat the substrates under controlledconditions according to a predetermined thermal recipe. These thermalrecipes fundamentally consist of a temperature that the semiconductorsubstrate must be heated to the rate of change of temperature, i.e., thetemperature ramp-up and ramp-down rates and the time that the thermalprocessing system remains at a particular temperature. For example,thermal recipes may require the substrate to be heated from roomtemperature to distinct temperatures of 1200° C. or more, for processingtimes at each distinct temperature ranging up to 60 seconds, or more.

Moreover, to meet certain objectives, such as minimal inter-diffusion ofmaterials between different regions of a semiconductor substrate, theamount of time that each semiconductor substrate is subjected to hightemperatures must be restricted. To accomplish this, the temperatureramp rates, both up and down, are preferably high. In other words, it isdesirable to be able to adjust the temperature of the substrate from alow to a high temperature, or visa versa, in as short a time aspossible.

The requirement for high temperature ramp rates led to the developmentof Rapid Thermal Processing (RTP), where typical temperature ramp-uprates range from 200 to 400° C./s, as compared to 5-15° C./minute forconventional furnaces. Typical ramp-down rates are in the range of80-150° C./s. A drawback of RTP is that it heats the entire wafer eventhough the IC devices reside only in the top few microns of the siliconwafer. This limits how fast one can heat up and cool down the wafer.Moreover, once the entire wafer is at an elevated temperature, heat canonly dissipate into the surrounding space or structures. As a result,today's state of the art RTP systems struggle to achieve a 400° C./sramp-up rate and a 150° C./s ramp-down rate.

To resolve some of the problems raised in conventional RTP typeprocesses various scanning laser anneal techniques have been used toanneal the surface(s) of the substrate. In general, these techniquesdeliver a constant energy flux to a small region on the surface of thesubstrate while the substrate is translated, or scanned, relative to theenergy delivered to the small region. Due to the stringent uniformityrequirements and the complexity of minimizing the overlap of scannedregions across the substrate surface these types of processes are noteffective for thermal processing contact level devices formed on thesurface of the substrate.

In view of the above, there is a need for an method for annealing asemiconductor substrate with high ramp-up and ramp-down rates. This willoffer greater control over the fabrication of smaller devices leading toincreased performance.

SUMMARY OF THE INVENTION

The present invention generally provide a method of thermally processinga substrate, comprising positioning a substrate on a substrate support,and delivering a plurality of electromagnetic energy pulses to firstarea on a surface of a substrate that is in thermal communication with afirst region of the substrate, wherein delivering a plurality ofelectromagnetic energy pulses comprises delivering a first pulse ofelectromagnetic energy to the surface of the substrate, delivering asecond pulse of electromagnetic energy to the surface of the substrate,and adjusting the time between the start of the first pulse and thestart of the second pulse so that the material contained in the firstregion melts.

Embodiments of the invention further provide a method of thermallyprocessing a substrate, comprising positioning a substrate on asubstrate support; and delivering electromagnetic energy to a surface ofa substrate that is in thermal communication with a first region and asecond region of the substrate, wherein delivering electromagneticenergy comprises delivering a first amount of electromagnetic energy ata first wavelength to preferentially melt a material contained in thefirst region rather than the second region, and delivering a secondamount of electromagnetic energy at a second wavelength topreferentially melt the material contained in the first region ratherthan the second region, wherein the delivering a second amount ofelectromagnetic energy and the delivering a first amount ofelectromagnetic energy overlap in time.

Embodiments of the invention further provide a method of thermallyprocessing a substrate, comprising positioning a substrate on asubstrate support, delivering electromagnetic energy to a first area ona surface of a substrate that is in thermal communication with a firstregion and a second region of the substrate, wherein deliveringelectromagnetic energy comprises delivering a first amount ofelectromagnetic energy at a first wavelength to preferentially melt amaterial contained in the first region rather than the second region,and delivering a second amount of electromagnetic energy at a firstwavelength to preferentially melt the material contained in the firstregion rather than the second region after the first amount ofelectromagnetic energy, and delivering electromagnetic energy to asecond area on the surface of the substrate that is in thermalcommunication with a third region and a fourth region of the substrate,wherein the second area is generally adjacent to the first area anddelivering electromagnetic energy comprises delivering a first amount ofelectromagnetic energy at a first wavelength to preferentially melt amaterial contained in the third region rather than the fourth region,and delivering a second amount of electromagnetic energy at a firstwavelength to preferentially melt the material contained in the thirdregion rather than the fourth region after the first amount ofelectromagnetic energy.

Embodiments of the invention further provide a method of thermallyprocessing a substrate, comprising delivering an amount ofelectromagnetic energy to a first area on a surface of a substrate tocause a material in one or more regions within the first area to melt,and delivering an amount of electromagnetic energy to a second area onthe surface of the substrate to cause a material in one or more regionswithin the second area to melt, wherein the first area and the secondarea on the surface of the substrate are generally adjacent to eachother.

Embodiments of the invention further provide a method of thermallyprocessing a substrate, comprising positioning a substrate on asubstrate support, and delivering electromagnetic energy to a surface ofa substrate that is in thermal communication with a first region andsecond region of the substrate, wherein delivering electromagneticenergy comprises adjusting the shape of a pulse of electromagneticenergy as a function of time to preferentially melt the materialcontained in the first region.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 illustrates an isometric view of an energy source that is adaptedto project an amount of energy on a defined region of the substratedescribed within an embodiment herein;

FIGS. 2A-2F illustrate a schematic side view of a region on a surface ofa substrate described within an embodiment herein;

FIG. 3A illustrate a graph of concentration versus depth into a regionof a substrate illustrated in FIG. 2A that is within an embodimentherein;

FIG. 3B illustrate a graph of concentration versus depth into a regionof a substrate illustrated in FIG. 2B that is within an embodimentherein;

FIG. 3C illustrate a graph of concentration versus depth into a regionof a substrate illustrated in FIG. 2C that is within an embodimentherein;

FIGS. 4A-4G schematic diagrams of electromagnetic energy pulsesdescribed within an embodiment herein;

FIGS. 5A-5C illustrate a schematic side view of a region on a surface ofa substrate described within an embodiment herein;

FIG. 6A illustrate methods of forming one or more desired layers on asurface of the substrate described within an embodiment containedherein;

FIGS. 6B-6D illustrate schematic side views of a region of a substratedescribed in conjunction with the method illustrated in FIG. 6A that iswithin an embodiment described herein;

FIG. 6E illustrate methods of forming one or more desired layers on asurface of the substrate described within an embodiment containedherein;

FIGS. 6F-6G illustrate schematic side views of a region of a substratedescribed in conjunction with the method illustrated in FIG. 6E that iswithin an embodiment described herein;

FIG. 7 illustrates a schematic side view of a region on the surface of asubstrate described within an embodiment herein;

FIG. 8 illustrates a schematic side view of a region on the surface of asubstrate described within an embodiment herein;

FIG. 9 illustrates a schematic side view of system that has an energysource that is adapted to project an amount of energy on a definedregion of the substrate described within an embodiment herein.

DETAILED DESCRIPTION

The present invention generally improves the performance of the implantanneal steps used in the process of manufacturing a semiconductordevices on a substrate. Generally, the methods of the present inventionmay be used to preferentially anneal selected regions of a substrate bydelivering enough energy to the selected regions to cause them tore-melt and solidify.

In general the term “substrates” as used herein can be formed from anymaterial that has some natural electrical conducting ability or amaterial that can be modified to provide the ability to conductelectricity. Typical substrate materials include, but are not limited tosemiconductors, such as silicon (Si) and germanium (Ge), as well asother compounds that exhibit semiconducting properties. Suchsemiconductor compounds generally include group III-V and group II-VIcompounds. Representative group III-V semiconductor compounds include,but are not limited to, gallium arsenide (GaAs), gallium phosphide(GaP), and gallium nitride (GaN). Generally, the term semiconductorsubstrates include bulk semiconductor substrates as well as substrateshaving deposited layers disposed thereon. To this end, the depositedlayers in some semiconductor substrates processed by the methods of thepresent invention are formed by either homoepitaxial (e.g., silicon onsilicon) or heteroepitaxial (e.g., GaAs on silicon) growth. For example,the methods of the present invention may be used with gallium arsenideand gallium nitride substrates formed by heteroepitaxial methods.Similarly, the invented methods can also be applied to form integrateddevices, such as thin-film transistors (TFTs), on relatively thincrystalline silicon layers formed on insulating substrates (e.g.,silicon-on-insulator [SOI] substrates).

In one embodiment of the invention, an amount of energy is delivered tothe surface of the substrate to preferentially melt certain desiredregions of the substrate to remove unwanted damage created from priorprocessing steps (e.g., crystal damage from implant processes), moreevenly distribute dopants in various regions of the substrate, and/oractivate various regions of the substrate. The preferential meltingprocesses will allow more uniform distribution of the dopants in themelted region, due to the increased diffusion rate and solubility of thedopant atoms in the moltent region of the substrate. The creation of amelted region thus allows: 1) the dopant atoms to redistribute moreuniformly, 2) defects created in prior processing steps to be removed,and 3) regions that have hyper-abrupt dopant concentrations to beformed. The gradient in dopant concentration in a region that has ahyper-abrupt dopant concentrations is very large (e.g., <2 nm/decade ofconcentration) as the concentration rapidly changes from one region toanother in the device.

Use of the techniques described herein allows junctions to be formedthat contain higher dopant concentrations than conventional devices,since the common negative attributes of the formed junctions, such as anincrease in the concentration of defects in the substrate material bythe increase in doping level, can be easily reduced to an acceptablelevel by use of the processing techniques described herein. The higherdopant levels and abrupt changes in the dopant concentration can thusincrease the conductivity of various regions of the substrate, thusimproving device speed without negatively affecting device yield, whileminimizing the diffusion of dopants into various regions of thesubstrate. The resultant higher dopant concentration increases theconductivity of the formed device and improves its performance.Typically, devices that are formed using an RTP process, will not use adopant concentration greater than about 1×10¹⁵ atoms/cm², since thehigher dopant concentrations cannot readily diffuse into the bulkmaterial of the substrate during typical RTP processes and will insteadresult in clusters of dopant atoms and other types of defects. Using oneor more of the embodiments of the anneal process described herein, muchmore dopant (up to 5-10 times more dopant, i.e., 1×10¹⁶ atoms/cm²) maybe successfully incorporated into the desired substrate surface, sinceregions of the substrate are preferentially melted so that the dopantswill become more evenly distributed throughout the liquid before theliquefied regions solidify.

FIG. 1 illustrates an isometric view of one embodiment of the inventionwhere an energy source 20 is adapted to project an amount of energy on adefined region, or a anneal region 12, of the substrate 10 topreferentially melt certain desired regions within the anneal region 12.In one example, as shown in FIG. 1, only one or more defined regions ofthe substrate, such as anneal region 12, are exposed to the radiationfrom the energy source 20 at any given time. In one aspect of theinvention, multiple areas of the substrate 10 are sequentially exposedto a desired amount of energy delivered from the energy source 20 tocause the preferential melting of desired regions of the substrate. Ingeneral, the areas on the surface of the substrate may be sequentiallyexposed by translating the substrate relative to the output of theelectromagnetic radiation source (e.g., conventional X/Y stage,precision stages) and/or translating the output of the radiation sourcerelative to the substrate. Typically, one or more conventionalelectrical actuators 17 (e.g., linear motor, lead screw and servomotor), which may be part of a separate precision stage (not shown), areused to control the movement and position of substrate 10. Conventionalprecision stages that may be used to support and position the substrate10, and heat exchanging device 15, may be purchased from Parker HannifinCorporation, of Rohnert Park, Calif.

In one aspect, the anneal region 12 is sized to match the size of thedie 13 (e.g., 40 “die” are shown in FIG. 1), or semiconductor devices(e.g., memory chip), that are formed on the surface of the substrate. Inone aspect, the boundary of the anneal region 12 is aligned and sized tofit within the “kurf” or “scribe” lines 10A that define the boundary ofeach die 13. In one embodiment, prior to performing the annealingprocess the substrate is aligned to the output of the energy source 20using alignment marks typically found on the surface of the substrateand other conventional techniques so that the anneal region 12 can beadequately aligned to the die 13. Sequentially placing anneal regions 12so that they only overlap in the naturally occurring unusedspace/boundaries between die 13, such as the scribe or kurf lines,reduces the need to overlap the energy in the areas where the devicesare formed on the substrate and thus reduces the variation in theprocess results between the overlapping anneal regions. This techniquehas advantages over conventional processes that sweep the laser energyacross the surface of the substrate, since the need to tightly controlthe overlap between adjacently scanned regions to assure uniformannealing across the desired regions of the substrate is not an issuedue to the confinement of the overlap to the unused space between die13. Confining the overlap to the unused space/boundary between die 13also improves process uniformity results versus conventional scanninganneal type methods that utilize adjacent overlapping regions thattraverse all areas of the substrate. Therefore, the amount of processvariation, due to the varying amounts of exposure to the energydelivered from the energy source 20 to process critical regions of thesubstrate is minimized, since any overlap of delivered energy betweenthe sequentially placed anneal regions 12 can be minimized. In oneexample, each of the sequentially placed anneal regions 12 are arectangular region that is about 22 mm by about 33 mm in size (e.g.,area of 726 square millimeters (mm²)). In one aspect, the area of eachof the sequentially placed anneal regions 12 formed on the surface ofthe substrate is between about 4 mm² (e.g., 2 mm×2 mm) and about 1000mm² (e.g., 25 mm×40 mm).

The energy source 20 is generally adapted to deliver electromagneticenergy to preferentially melt certain desired regions of the substratesurface. Typical sources of electromagnetic energy include, but are notlimited to an optical radiation source (e.g., laser), an electron beamsource, an ion beam source, and/or a microwave energy source. In oneaspect, the substrate 10 is exposed to a pulse of energy from a laserthat emits radiation at one or more appropriate wavelengths for adesired period of time. In one aspect, pulse of energy from the energysource 20 is tailored so that the amount of energy delivered across theanneal region 12 and/or the amount of energy delivered over the periodof the pulse is optimized to enhance preferential melting of certaindesired areas. In one aspect, the wavelength of the laser is tuned sothat a significant portion of the radiation is absorbed by a siliconlayer disposed on the substrate 10. For laser anneal process performedon a silicon containing substrate, the wavelength of the radiation istypically less than about 800 nm, and can be delivered at deepultraviolet (UV), infrared (IR) or other desirable wavelengths. In oneembodiment, the energy source 20 is an intense light source, such as alaser, that is adapted to deliver radiation at a wavelength betweenabout 500 nm and about 11 micrometers. In either case, the annealprocess generally takes place on a given region of the substrate for arelatively short time, such as on the order of about one second or less.

In one aspect, the amount of energy delivered to the surface of thesubstrate is configured so that the melt depth does not extend beyondthe amorphous depth defined by the amorphization implant step. Deepermelt depths facilitate the diffusion of dopant from the doped amorphouslayers into the undoped molten layers. Such undesirable diffusion wouldsharply and deleteriously alter the electrical characteristics of thecircuits on the semiconductor substrate. In some anneal processes,energy is delivered to the surface of a substrate for a very short timein order to melt the surface of the substrate to a sharply defineddepth, for example less than 0.5 micrometers. The exact depth isdetermined by the size of the electronic device being manufactured.

Temperature Control of the Substrate During the Anneal Process

In one embodiment, it may be desirable to control the temperature of thethermally substrate during thermal processing by placing a surface ofthe substrate 10, illustrated in FIG. 1, in thermal contact with asubstrate supporting surface 16 of a heat exchanging device 15. The heatexchanging device 15 is generally adapted to heat and/or cool thesubstrate prior to or during the annealing process. In thisconfiguration, the heat exchanging device 15, such as a conventionalsubstrate heater available from Applied Materials Inc., Santa Clara,Calif., may be used to improve the post-processing properties of theannealed regions of the substrate. In general, the substrate 10 isplaced within an enclosed processing environment (not shown) of aprocessing chamber (not shown) that contains the heat exchanging device15. The processing environment within which the substrate resides duringprocessing may be evacuated or contain an inert gas that has a lowpartial pressure of undesirable gases during processing, such as oxygen.

In one embodiment, the substrate may be preheated prior to performingthe annealing process so that the energy required to reach the meltingtemperature is minimized, which may reduce any induced stress due to therapid heating and cooling of the substrate and also possibly reduce thedefect density in the resolidified areas of the substrate. In oneaspect, the heat exchanging device 15 contains resistive heatingelements 15A and a temperature controller 15C that are adapted to heat asubstrate disposed on a substrate supporting surface 16. The temperaturecontroller 15C is in communication with the controller 21 (discussedbelow). In one aspect, it may be desirable to preheat the substrate to atemperature between about 20° C. and about 750° C. In one aspect, wherethe substrate is formed from a silicon containing material it may bedesirable to preheat the substrate to a temperature between about 20° C.and about 500° C.

In another embodiment, it may be desirable to cool the substrate duringprocessing to reduce any interdiffusion due to the energy added tosubstrate during the annealing process and/or increase the regrowthvelocity after melting to increase the amorphization of the variousregions during processing, such as described in conjunction with FIG. 8.In one configuration, the heat exchanging device 15 contains one or morefluid channels 15B and a cryogenic chiller 15D that are adapted to coola substrate disposed on a substrate supporting surface 16. In oneaspect, a conventional cryogenic chiller 15D, which is in communicationwith the controller 21, is adapted to deliver a cooling fluid throughthe one or more fluid channels 15B. In one aspect, it may be desirableto cool the substrate to a temperature between about −240° C. and about20° C.

The controller 21 (FIG. 1) is generally designed to facilitate thecontrol and automation of the thermal processing techniques describedherein and typically may includes a central processing unit (CPU) (notshown), memory (not shown), and support circuits (or I/O) (not shown).The CPU may be one of any form of computer processors that are used inindustrial settings for controlling various processes and hardware(e.g., conventional electromagnetic radiation detectors, motors, laserhardware) and monitor the processes (e.g., substrate temperature,substrate support temperature, amount of energy from the pulsed laser,detector signal). The memory (not shown) is connected to the CPU, andmay be one or more of a readily available memory, such as random accessmemory (RAM), read only memory (ROM), floppy disk, hard disk, or anyother form of digital storage, local or remote. Software instructionsand data can be coded and stored within the memory for instructing theCPU. The support circuits (not shown) are also connected to the CPU forsupporting the processor in a conventional manner. The support circuitsmay include conventional cache, power supplies, clock circuits,input/output circuitry, subsystems, and the like. A program (or computerinstructions) readable by the controller determines which tasks areperformable on a substrate. Preferably, the program is software readableby the controller and includes code to monitor and control the substrateposition, the amount of energy delivered in each electromagnetic pulse,the timing of one or more electromagnetic pulses, the intensity andwavelength as a function of time for each pulse, the temperature ofvarious regions of the substrate, and any combination thereof.

Selective Melting

In an effort to minimize inter-diffusion between various regions of aformed device, remove defects in the substrate material, and more evenlydistribute dopants in various regions of the substrate, one or moreprocessing steps are performed on various regions of the substrate tocause them to preferentially remelt when exposed to energy deliveredfrom an energy source during the anneal process. The process ofmodifying the properties of a first region of the substrate so that itwill preferentially melt rather than a second region of the substrate,when they are both exposed to about the same amount energy during theannealing process, is hereafter described as creating a melting pointcontrast between these two regions. In general, the substrate propertiesthat can be modified to allow preferential melting of desired regions ofthe substrate include implanting, driving-in and/or co-depositing one ormore elements within a desired regions of the substrate, creatingphysical damage to desired regions of the substrate, and optimizing theformed device structure to create the melting point contrast in desiredregions of the substrate. Each of these modification processes will bereviewed in turn.

FIGS. 2A-2C illustrate cross-sectional views of an electronic device 200at different stages of a device fabrication sequence incorporating oneembodiment of the invention. FIG. 2A illustrates a side view of typicalelectronic device 200 formed on a surface 205 of a substrate 10 that hastwo doped regions 201 (e.g., doped regions 201A-201B), such as a sourceand drain region of a MOS device, a gate 215, and a gate oxide layer216. The doped regions 201A-201B are generally formed by implanting adesired dopant material into the surface 205 of the substrate 10. Ingeneral, typical n-type dopants (donor type species) may include arsenic(As), phosphorus (P), and antimony (Sb), and typical p-type dopants(acceptor type species) may include boron (B), aluminum (Al), and indium(In) that are introduced into the semiconductor substrate 10 to form thedoped regions 201A-201B. FIG. 3A illustrates an example of theconcentration of the dopant material as a function of depth (e.g., curveC₁), from the surface 205 and into the substrate 10 along a path 203extending through the doped region 201A. The doped region 201A has ajunction depth D₁ after the implant process, which may be defined as apoint where the dopant concentration drops off to a negligible amount.It should be noted that FIGS. 2A-2F are only intended to illustrate someof the various aspects of the invention and is not intended to belimiting as to the type of device, type of structure, or regions of adevice that may be formed using the various embodiments of the inventiondescribed herein. In one example, the doped regions 201 (e.g., source ordrain regions in a MOS device) can be a raised or lowered relative tothe position of the gate 215 (e.g., gate in a MOS device) withoutvarying from the scope of the invention described herein. Assemiconductor device sizes decrease the position and geometry ofstructural elements of the electronic devices 200 formed on the surface205 of a substrate 10 may vary to improve device manufacturability ordevice performance. It should also be noted that the modification ofonly a single doped region 201A, as shown in FIGS. 2A-2E, is notintended to be limiting as to the scope of the invention describedherein and is only meant to illustrate how embodiments of the inventioncan be used to manufacture a semiconductor device.

FIG. 2B illustrates a side view of the electronic device 200 shown inFIG. 2A during a process step that is adapted to selectively modify theproperties of a discrete region (e.g., modified area 210) of thesubstrate 10, which in this case is a region containing a single dopedregion 201A, to create a melting point contrast. After performing themodification process a melting point contrast will be created betweenthe modified area 210 and unmodified areas 211. In one embodiment, themodification process includes the step(s) of adding a material to alayer as it is being deposited on the surface of the substrate, wherethe incorporated material is adapted to form an alloy with the substratematerial to lower the melting point of a region 202 within the modifiedarea 210. In one aspect, the incorporated material is added to thedeposited layer during an epitaxial layer deposition process.

In another embodiment, the modification process includes the step ofimplanting (see “A” in FIG. 2B) a material that is adapted to form analloy with the substrate material to lower the melting point of a region202 within the modified area 210. In one aspect, the modificationprocess is adapted to implant the alloying material to a depth D₂, asshown in FIG. 2B. FIG. 3B illustrates an example of the concentration ofthe dopant material (e.g., curve C₁) and implanted alloying material(e.g., curve C₂) as a function of depth, from the surface 205 andthrough the substrate 10 along a path 203. In one aspect, where thesubstrate 10 is formed from a silicon containing material and theimplanted alloying materials that may be used include, for example,germanium (Ge), arsenic (As), gallium (Ga), carbon (C), tin (Sn), andantimony (Sb). In general, the alloying material can be any materialthat when heated in the presence of the substrate base material causesthe melting point of the region 202 in the modified area 210 to belowered relative to the unmodified areas 211. In one aspect, a region ofa silicon substrate is modified by the addition of between about 1% andabout 20% of germanium to reduce the melting point between the modifiedand un-modified area. It is believed that the addition of germanium inthese concentrations will lower the melting point of the modified areasversus the un-modified areas by about 300° C. In one aspect, the region202 formed in a silicon substrate contains germanium (Ge) and carbon(C), so that a Si_(x)Ge_(y)C_(z) alloy will form to lower the meltingpoint of the region 202 relative to the unmodified areas 211. In anotheraspect, a region of a silicon substrate is modified by the addition ofabout 1% or less of arsenic to reduce the melting point between themodified and un-modified area.

In another embodiment, the modification process includes the step ofinducing some damage to the substrate 10 material in the variousmodified areas (e.g., modified area 210) to damage the crystal structureof the substrate, and thus make these regions more amorphous. Inducingdamage to the crystal structure of the substrate, such as damaging asingle crystal silicon substrate, will reduce the melting point of thisregion relative to an undamaged region due to the change in the bondingstructure of atoms in the substrate and thus induce thermodynamicproperty differences between the two regions. In one aspect, damage tothe modified area 210 in FIG. 2B is performed by bombarding the surface205 of the substrate 10 (see “A” in FIG. 2B) with a projectile that cancreate damage to the surface of the substrate. In one aspect, theprojectile is a silicon (Si) atom that is implanted into a siliconcontaining substrate to induce damage to the region 202 within themodified area 210. In another aspect, the damage to the substratematerial is created by bombarding the surface with gas atoms, such asargon (Ar), krypton (Kr), xenon (Xe) or even nitrogen (N₂), using animplant process, an ion beam or biased plasma to induce damage to region202 of the modified area 210. In one aspect, the modification process isadapted to create a region 202 that has induced damage to a depth D₂, asshown in FIG. 2B. It is believed that a dislocation or vacancy densityof between about 5×10¹⁴ and about 1×10¹⁶ /cm² may be useful to createthe melting point contrast between a modified area 210 versus anunmodified area 211. In one aspect, FIG. 3B illustrates an example ofthe concentration of the dopant material (e.g., curve C₁) and defectsdensity (e.g., curve C₂) as a function of depth, from the surface 205and through the substrate 10 along a path 203.

It should be noted that while FIGS. 2A-2B illustrate a process sequencein which the modification process is performed after the doping process,this process sequence is not intended to be limiting as to the scope ofthe invention described herein. For example, in one embodiment, it isdesirable to perform the modification process described in FIG. 2B priorto performing the doping process described in FIG. 2A.

FIG. 2C illustrates a side view of the electronic device 200 shown inFIG. 2B that is exposed to radiation “B” emitted from the an energysource, such as optical radiation from a laser. During this step themodified area(s) (e.g., modified area 210) and unmodified areas (e.g.,211) disposed across the substrate 10 are exposed to an amount of energywhich causes the region 202 in the modified area(s) 210 to selectivelymelt and resolidify after the pulse of radiation “B” has been applied,while the unmodified areas 211 remain in a solid state. The amount ofenergy, the energy density and the duration that the radiation “B” isapplied can be set to preferentially melt the regions 202 by knowing thedesired depth of the region 202, the materials used to create the region202, the other materials used to form the electronic device 200, and theheat transfer characteristics of the components within the formedelectronic device 200. As shown in FIGS. 2C and 3C, upon exposure to theradiation “B” the remelting and solidification of the region 202 causesthe concentration of the dopant atoms (e.g., curve C₁) and alloyingatoms (e.g., curve C₂) is more uniformly redistributed in the region202. Also, the dopant concentration between the region 202 and thesubstrate bulk material 221 has a sharply defined boundary (i.e., a“hyper-abrupt” junction) and thus minimizes the unwanted diffusion intothe substrate bulk material 221. In the embodiment, discussed above, inwhich damage is induced into the substrate 10 to improve the meltingpoint contrast the concentration of defects (e.g., curve C₂) afterresolidification will preferably drop to a negligible level.

Thermal Isolation Techniques

In another embodiment, the various thermal properties of differentregions of the formed device are tailored to preferentially cause themelting in one region versus another region. In one aspect, the meltingpoint contrast is created by forming different regions of the devicewith materials that have different thermal conductivities (k). It shouldbe noted that heat transferred by conduction is governed by theequation:

Q=kAΔT/Δx

in which Q is the time rate of heat flow through a body, k is theconductivity constant dependent on the nature of the material and thematerial temperature, A is the area through which the heat flows, Δx isthe thickness of the body of matter through which the heat is passing,and ΔT is the temperature difference through which the heat is beingtransferred. Therefore, since k is a property of the material theselection or modification of the material in various regions of thesubstrate can allow one to control the heat flow into and out-of thedifferent regions of the substrate to increase the melting pointcontrast for the various regions. In other words, where the material ina region of a substrate has a higher thermal conductivity than thematerial in other regions, it will lose more thermal energy viaconductive losses during a laser anneal process, and, hence, will notreach the same temperatures that another region that has a lower thermalconductivity will reach. The regions in intimate contact with the higherthermally conductive regions can be prevented from melting, while otherregions in intimate contact with lower thermal conductivity regions willreach their melting point during the laser anneal process. Bycontrolling the thermal conductivity of the various regions of theelectronic device 200 the melting point contrast can be increased. Thecreation of regions having varying thermal conductivities may beperformed by performing conventional deposition, patterning and etchingtechniques in various underlying layers of the electronic device 200 tocreate these regions having different thermal conductivities. Theunderlying layers having differing thermal conductivities may be formedby use of conventional chemical vapor deposition (CVD) processes, atomiclayer deposition (ALD) processes, implant processes, and epitaxialdeposition techniques.

FIG. 2D illustrates a side view of the electronic device 200 that is hasa buried region 224 that has a lower thermal conductivity than thesubstrate bulk material 221. In this case the radiation “B” emitted froman energy source, is absorbed at the surface 205 of the substrate and isconducted through the substrate 10, so that the heat flow (Q₁) in theregion above (e.g., doped region 201A) the buried region 224 is lessthan the heat flow (Q₂) from an area that doesn't have the lowerconductivity buried layer. Therefore, since the heat lost from theregion above the buried region 224 is less than the other regions of thesubstrate, this area will reach a higher temperature than the otherregions of the device. By controlling the amount of energy delivered bythe energy source 20 the temperature in the regions above the buriedlayer can be raised to a level that will cause it to preferentially meltversus the other regions. In one aspect, the buried region 224 is madeof an insulative material, such as a silicon dioxide (SiO₂), siliconnitride (SiN), germanium (Ge), gallium arsenide (GaAs), combinationsthereof or derivatives thereof. So although the actual melting point ofthe substrate material in the region that is to be melted is notaltered, there is still a quantifiable and repeatable contrast inthermal behavior from other regions of the substrate surface that allowsit to be selectively melted. In another embodiment, the buried region224 may have a higher conductivity than the substrate bulk material 221,which may then allow the areas that do not have the buried layer topreferentially melt versus the regions above the buried layer.

Modification of Surface Properties

In one embodiment, the properties of the surface over the variousregions 202 of the substrate 10 are altered to change the melting pointcontrast between one or more desired regions. In one aspect, theemissivity of the surface of the substrate in a desired region isaltered to change the amount of energy transferred from the substratesurface during processing. In this case, a region that has a loweremissivity than another region will achieve a higher processingtemperature due to its inability to reradiate the absorbed energyreceived from the energy source 20. When performing an anneal processthat involves the melting of the surface of a substrate, the processingtemperatures achieved at the surface of the substrate can be quite high(e.g., ˜1414° C. for silicon), and thus the effect of varying theemissivity can have a dramatic effect on the melting point contrast,since radiative heat transfer is the primary heat loss mechanism.Therefore, variations in the emissivity of different regions of thesubstrate surface may have a significant impact on the ultimatetemperatures reached by the various regions of the substrate. Regionswith low emissivity may be elevated above the melting point during theannealing process, while regions with high emissivity that have absorbedthe same amount of energy may remain substantially below the meltingpoint. Varying the emissivity of the various surfaces, or emissivitycontrast, may be accomplished via selective deposition of a low- orhigh-emissivity coating onto the substrate surface, and/or modifying thesurface of the substrate (e.g., surface oxidation, surface roughening).

In one embodiment, the reflectivity of the surface of the substrate inone or more regions is altered to change the amount of energy absorbedwhen the substrate 10 is exposed to energy from the energy source. Byvarying the reflectivity of the surface of the substrate the amount ofenergy absorbed and thus the maximum temperature achieved by thesubstrate in a region at and below the substrate surface will differbased on the reflectivity. In this case a surface having a lowerreflectivity will more likely melt than another region that has a higherreflectivity. Varying the reflectivity of the surface of the substratemay be accomplished via selective deposition of a low- orhigh-reflectance coating onto the substrate surface, and/or modifyingthe surface of the substrate (e.g., surface oxidation, surfaceroughening). A highly absorbing (non-reflective) coating may beselectively applied to regions that are intended to be melted during theanneal process.

FIG. 2E illustrates one embodiment in which a coating 225 is selectivelydeposited, or uniformly deposited and then selectively removed, to leavea layer that has a different emissivity and/or reflectivity than theother regions on the surface 205 of the substrate 10. In this case theheat flow (Q₁) in the doped region 201A, below the coating 225, can beadjusted based on the properties of the coating versus the energyabsorbed (Q₂) in other regions of the substrate. In this way the heatloss (Q₃) or reflected from the coating 225 can be varied versus theheat lost (Q₄) from the other regions. In one aspect, a carboncontaining coating is deposited on the substrate surface by use of a CVDdeposition process.

FIG. 2F illustrates one embodiment in which a coating 226 that altersthe optical properties of the surface of the substrate (e.g.,emissivity, reflectivity) is deposited over the surface of thesubstrate, for example over the device shown in FIG. 2A, and then anamount of material is removed to create regions that have differingoptical properties. For example, as shown in FIG. 2F, the coating 226has been removed from the surface of the gate 215, thus leaving thesurface of the coating 226 and the surface 205 of the gate exposed tothe incident radiation “B.” In this case, the coating 226 and thesurface 205 of the gate have different optical properties, such as adifferent emissivity and/or a different reflectivity. The removalprocess used to expose or create regions that have differing opticalproperties may be performed by use of a conventional material removalprocess, such as a wet etch or chemical mechanical polishing (CMP)process. In this case the absorption and heat flow (Q₁) in the dopedregions 201A-201B, below the coating 226, can be adjusted based on theproperties of the coating versus the absorption and heat flow (Q₂) ingate 215 region of the substrate. In this way the heat loss (Q₃) orreflected from the coating 226 can be varied versus the heat loss (Q₄)or reflected from the gate 215 region.

In one embodiment, the coating 226 contains one or more deposited layersof a desired thickness that either by themselves or in combinationmodify the optical properties (e.g., emissivity, absorbance,reflectivity) of various regions of the substrate that are exposed toone or more wavelengths of incident radiation. In one aspect, thecoating 226 contains layers that either by themselves or in combinationpreferentially absorb or reflect one or more wavelengths of the incidentradiation “B.” In one embodiment, the coating 226 contains a dielecticmaterial, such as fluorosilicate glass (FSG), amorphous carbon, silicondioxide, silicon carbide, silicon carbon germanium alloys (SiCGe),nitrogen containing silicon carbide (SiCN), a BLOk™ dielectric materialmade by a process that is commercially available from Applied Materials,Inc., of Santa Clara, or a carbon containing coating that is depositedon the substrate surface by use of a chemical vapor deposition (CVD)process or atomic layer deposition process (ALD) process. In one aspect,coating 226 contains a metal, such as but not limited to titanium (Ti),titanium nitride (TiN), tantalum (Ta), cobalt (Co), or ruthenium (Ru).

It should be noted that one or more of the various embodiments,discussed herein, may be used in conjunction with each other in order tofurther increase process window. For example, a selectively deposited,light absorbing coating may be used in conjunction with doping ofcertain defined regions to broaden the process window of the annealprocess.

Tuning the Energy Source Output to Achieve Preferential Melting

As noted above, the energy source 20 is generally adapted to deliverelectromagnetic energy to preferentially melt certain desired regions ofthe substrate 10. Typical sources of electromagnetic energy include, butare not limited to an optical radiation source (e.g., laser (UV, IR,etc. wavelengths)), an electron beam source, an ion beam source, and/ora microwave energy source. In one embodiment of the invention, theenergy source 20 is adapted to deliver optical radiation, such as alaser, to selectively heat desired regions of a substrate to the meltingpoint.

In one aspect, the substrate 10 is exposed to a pulse of energy from alaser that emits radiation at one or more appropriate wavelengths, andthe emitted radiation has a desired energy density (W/cm²) and/or pulseduration to enhance preferential melting of certain desired regions. Forlaser annealing processes performed on a silicon containing substrate,the wavelength of the radiation is typically less than about 800 nm. Ineither case, the anneal process generally takes place on a given regionof the substrate for a relatively short time, such as on the order ofabout one second or less. The desired wavelength and pulse profile usedin an annealing process may be determined based on optical and thermalmodeling of the laser anneal process in light of the material propertiesof the substrate.

FIGS. 4A-4D illustrate various embodiments in which the variousattributes of the pulse of energy delivered from an energy source 20 toan anneal region 12 (FIG. 1) is adjusted as a function of time toachieve improved melting point contrast, and improve the anneal processresults. In one embodiment, it is desirable to vary the shape of a laserpulse as a function of time, and/or vary the wavelengths of thedelivered energy to enhance the heat input into regions of the substrateintended to be melted and minimize the heat input into other regions. Inone aspect, it may also be desirable to vary the energy delivered to thesubstrate.

FIG. 4A graphically illustrates a plot of delivered energy versus timeof a single pulse of electromagnetic radiation (e.g., pulse 401) thatmay be delivered from the energy source 20 to the substrate 10 (see FIG.1). The pulse illustrated in FIG. 4A is generally a rectangular pulsethat delivers a constant amount of energy (E₁) for the complete pulseduration (t₁).

In one aspect, the shape of the pulse 401 may be varied as a function oftime as it is delivered to the substrate 10. FIG. 4B graphicallyillustrates a plot of two pulses 401A, 401B of electromagnetic radiationthat may be delivered from one energy source 20 to the substrate 10 thathave a different shape. In this example, each pulse may contain the sametotal energy output, as represented by the area under each curve, butthe effect of exposing regions of the substrate 10 to one pulse versusanother pulse may improve the melting point contrast experienced duringthe anneal process. Therefore, by tailoring the shape, peak power leveland/or amount of energy delivered in each pulse the anneal process maybe improved. In one aspect, the pulse is gaussian shaped.

FIG. 4C graphically illustrates a pulse of electromagnetic radiation(e.g., pulse 401) that is trapezoidal in shape. In this case, in twodifferent segments (e.g., 402 and 404) of the pulse 401 the energydelivered is varied as a function of time. While FIG. 4C illustrates apulse 401 profile, or shape, in which the energy versus time varies in alinear fashion, this is not intended to be limiting as to the scope ofthe invention since the time variation of the energy delivered in apulse may, for example, have a second degree, third degree, or fourthdegree shaped curve. In another aspect, the profile, or shape, of theenergy delivered in a pulse as a function of time may be a second order,a third order, or exponential-shaped curve. In another embodiment, itmay be advantageous to use a pulse having different shapes (e.g.,rectangular and triangular modulation pulse, sinusoidal and rectangularmodulation pulse, rectangular, triangular and sinusoidal modulationpulse, etc.) during processing to achieve the desired annealing results.

Depending on the properties of the various regions of the device theshape of the delivered pulse of electromagnetic radiation may betailored to improve the anneal process results. Referring to FIG. 4B,for example, in some situations in which various regions of a substratethat are to be melted during the anneal process are thermally isolatedfrom other regions of the device by areas that have a low thermalconductivity, use of a pulse having a shape similar to pulse 401B may beadvantageous. A pulse having a longer duration may be advantageous,since the more thermally conductive material regions of the substratewill have more time to dissipate the heat by conduction, while theregions that are to be melted are more thermally isolated thus allowingthe temperature in the regions that are to be melted to rise to amelting point temperature. In this case the duration, peak power leveland total energy output of the pulse can be appropriately selected, sothat the areas that are not intended to melt will not reach theirmelting point. The process of tailoring the shape of the pulse may alsobe advantageous when surfaces of varying emissivity are used to create amelting point contrast.

Referring to FIG. 4C, in one embodiment, the slope of the segment 401,the shape of the segment 401, the shape of the segment 403, the time ata power level (e.g., segment 403 at the energy level E₁), the slope ofthe segment 404, and/or the shape of the segment 404 are adjusted tocontrol the annealing process. It should be noted that it is generallynot desirable to cause the material within the annealed regions tovaporize during processing due to particle and process resultvariability concerns. It is therefore desirable to adjust the shape ofthe pulse of energy to rapidly bring the temperature of the annealedregion to it melting point without superheating the region and causingvaporization of the material. In one embodiment, as shown FIG. 4G, theshape of the pulse 401 may adjusted so that it has multiple segments(i.e., segments 402, 403A, 403B, 403C, and 404) are used to rapidlybring the anneal region to its melting point and then hold the materialin a molten state for a desired period of time (e.g., t₁), whilepreventing vaporization of material within the annealing region. Thelength of time, the shape of the segments and the duration of each ofthe pulse segments may vary as the size, melt depth, and the materialcontained within the annealing regions is varied.

In another aspect, multiple wavelengths of radiant energy may becombined to improve the energy transfer to the desired regions of thesubstrate to achieve an improved melting point contrast, and/or improvethe anneal process results. In one aspect, the amount of energydelivered by each of the combined wavelengths is varied to improve themelting point contrast, and improve the anneal process results. FIG. 4Dillustrates one example in which a pulse 401 contains two wavelengthsthat may deliver differing amounts of energy per unit time to asubstrate 10 in order to improve the melting point contrast and/orimprove the anneal process results. In this example, a frequency F1 isapplied to the substrate at a constant level over the period of thepulse and another frequency F2 is applied to the substrate 10 at aconstant level for most of the period except for a portion that peaksfor a period of time during the period of the pulse.

FIG. 4E graphically illustrates a plot of a pulse 401 that has twosequential segments that deliver energy at two different frequencies F3and F4. Therefore, since various regions of the substrate may absorbenergy at different rates at different wavelengths the use of pulse thatcontains multiple wavelengths that can deliver variable amounts ofenergy, as shown in FIGS. 4D and 4E, may be advantageous to achievedesirable annealing process results.

In one embodiment, two or more pulses of electromagnetic radiation aredelivered to a region of the substrates at differing times so that thetemperature of regions on the substrate surface can be easilycontrolled. FIG. 4F graphically illustrates a plot of two pulses 401Aand 401B that are delivered a varying distance in time apart, or period(t), to selectively melt certain regions on the surface of a substrate.In this configuration, by adjusting the period (t) between thesubsequent pulses, the peak temperature reached by regions on thesubstrate surface can be easily controlled. For example, by reducing theperiod (t), or frequency, between pulses the heat delivered in the firstpulse 401A has less time to dissipate the heat before the second pulse401B is delivered, which will cause the peak temperature achieved in thesubstrate to be higher than when the period between pulses is increased.In this way by adjusting the period the energy and melt temperature canbe easily controlled. In one aspect, it may desirable to assure thateach pulse by itself does not contain enough energy to cause thesubstrate to reach the melt temperature, but the combination of thepulses causes the regions 202 to reach the melt temperature. Thisprocess of delivering multiple pulses, such as two or more pulses, willtend to reduce the thermal shock experienced by the substrate materialversus delivering a single pulse of energy. Thermal shock can lead todamage of the substrate and generate particles that will create defectsin subsequent processing steps performed on the substrate.

Referring to FIG. 4F, in one embodiment, two or more energy sources,such as lasers, are operated in sequence so as to shape the thermalprofile of the surface of a substrate as a function of time. Forexample, one laser or an array of lasers may deliver a pulse 401A thatelevates the surface of the substrate to a temperature T₀ for a time t₁.Prior to or at the end of t₁, a second pulse 402B is delivered from asecond laser, or from multiple lasers operating in tandem, that bringsthe substrate temperature to a temperature T₁ for a time t₂. The thermalprofile can thus be shaped by controlling the sequencing pulses ofenergy delivered from the multiple lasers. This process may have thermalprocessing benefits, such as but not limited to the application ofcontrolling dopant diffusion and the direction of the dopant diffusion.

Electromagnetic Radiation Pulses

For the purpose of delivering sufficient electromagnetic radiation(light) to the surface of a silicon containing substrate, or substratecomprised of another material requiring thermal processing, thefollowing a process controls may be used.

In one embodiment, two or more electromagnetic energy sources, such aslasers, are operated in sequence so as to shape the thermal profile ofthe surface being thermally processed and where the lasers are operatedin such a manner as to correct for pulse-to-pulse energy variations. Inone aspect, the source 20, schematically illustrated in FIGS. 1 and 9,contains two or more electromagnetic energy sources, such as but notlimited to an optical radiation source (e.g., laser), an electron beamsource, an ion beam source, and/or a microwave energy source. Thepulse-to-pulse energy from a device such as a pulsed laser may have apercent variation of each pulse. The variation in pulse energy may beunacceptable for the substrate thermal process. To correct for thispulse variation, one or more laser(s) deliver a pulse that elevates thesubstrate temperature. Then an electronic controller (e.g., controller21 in FIG. 1), which is adapted to monitor the pulses delivered and theenergy, or rise time, of the pulse that is in delivery, then is used tocalculate the amount of energy required to “trim” or adjust the thermalprofile (e.g., temperature of a region of the substrate as a function oftime) so that it is within process targets and command a second smallerlaser or series of smaller lasers to deliver the final energy tocomplete the thermal processing. The electronic controller generallyuses one or more conventional radiation detectors to monitor the energyand/or wavelength of pulses delivered to the substrate. The smallerlasers may also have peak-to-peak variation in pulse output energy, butbecause they deliver substantially less energy per pulse than theinitial pulse (or pulses) at the start of the surface treatment thiserror will generally be within process limits. The electronic controlleris thus adapted to compensate for the variation in energy delivered by apulse, and thus assure that a desired energy level is delivered duringthe thermal process.

In one aspect, the two or more energy sources, discussed above, may alsobe implemented using a single color (wavelength) of laser light with abandwidth of color frequency, multiple wavelengths, single or multipletemporal and spatial laser modes, and polarization states.

The output of the laser or lasers will likely not have the correctspatial and temporal energy profile for delivery to the substratesurface. Therefore, a system using microlenses to shape the output ofthe lasers is used to create a uniform spatial energy distribution atthe substrate surface. Selection of glass types and geometry of themicrolenses may compensate for thermal lensing effects in the opticaltrain necessary for delivering the pulsed laser energy to the substratesurface.

High frequency variations in pulse energy at the substrate surface,known as speckle, is created by neighboring regions of constructive anddestructive phase interference of the incident energy. Specklecompensation may include the following: a surface acoustic wave devicefor rapidly varying the phase at the substrate such that this rapidvariation is substantially faster than the thermal processing time ofthe laser pulse or pulses; pulse addition of laser pulses; alternatingpolarization of laser pulses for example, delivery of multiplesimultaneous or delayed pulses that are linearly polarized but havetheir polarization states (e-vectors) in a nonparallel condition.

Thermal Stabilizing Structures Formed on a Patterned Substrate

In one embodiment, as shown in FIGS. 5A-5C, a homogenizing layer (item110 in FIG. 5B) is deposited on a surface of the substrate to reduce thevariations in the depth, or volume, of the silicon region 112 meltedwhen surface of the substrate is exposed to electromagnetic energy 150delivered from an electromagnetic radiation source (not shown). Thevariation in the depth, or volume, of the region melted is affected bythe variations in the mass density of the various regions of thepatterned substrate, the absorption coefficient of the material on whichthe radiant energy impinges, and the various physical and thermalproperties of the material (e.g., thermal conductivity, heat capacity,thickness of the material). In general the electromagnetic radiationsource is designed to deliver electromagnetic energy to the surface ofsubstrate to thermally process or anneal portions of the substratesurface. Typical electromagnetic radiation sources may include, but arenot limited to optical radiation sources (e.g., lasers), electron beams,ion beams, or microwave sources.

The device structure formed on a surface 102 of the substrate 100illustrated in FIGS. 5A-5C and 6A-6C are not intended to be limiting asto the scope of the invention described herein, since, for example, thesilicon region 112 (e.g., source or drain regions in a MOS device) canbe a raised or lowered relative to the position of the features 101(e.g., gate in a MOS device) without varying from the scope of theinvention described herein. As semiconductor device sizes decrease theposition and geometry of structural elements of the devices formed onthe surface of a substrate vary to improve device manufacturability ordevice performance.

FIG. 5A illustrates a cross-sectional view of a substrate 100 that has aplurality of features 101 and silicon regions 112 formed on a surface102 of the substrate 100. As shown in FIG. 5A the surface 102 hasmultiple features 101 that are laterally spaced a varying distanceapart. In one aspect, the features 101 are “gates” and the siliconregions 112 are “source and drain regions” used to form a metal oxidesemiconductor (MOS) device on the substrate surface. In theconfiguration shown in FIG. 5A the incident electromagnetic energy 150impinges the surface 102 causing the some regions of the surface 102 ofthe substrate to absorb the incident energy and possibly form meltregions 113. The physical, thermal and optical properties of the variousmaterials exposed to the incident electromagnetic energy 150 willdetermine whether the various areas on the surface 102 will melt uponexposure to the delivered energy. It is believed that when the features101 are polysilicon gates the absorption energy from a laser, atwavelengths <800 nm, will be significantly less than the energy absorbedby the silicon regions 112 that contain N-type or P-type doped silicon,such as found in a source or drain region of a MOS device. Therefore, itis believed that due to the heat capacity and thermal mass of thefeatures 101, and their relative position to the silicon regions 112,the delivered electromagnetic energy 150 in the areas adjacent to thefeatures 101 will remain cooler due to the diffusion of heat away fromthe melt region 113. The loss of heat to the features 101 will reducethe energy available to form the melt region 113 and thus affect thedepth and/or volume, of the melt region 113. Therefore, there is a needfor a way to reduce the variation in pattern density on the surface ofthe substrate.

FIG. 5B illustrates a cross-sectional view of a substrate 100 that has aplurality of features 101, silicon regions 112 and a homogenizing layer120 formed on a surface 102 of the substrate 100. FIG. 5B is similar toFIG. 5A except the addition of the homogenizing layer 120. In generalthe homogenizing layer 120 is used to make the heat capacity of thesurface 102 of the substrate 100 more uniform. In one embodiment, thethickness and material from which the homogenizing layer 120 is formedis selected to balance the heat capacity of the surface of the substrateto reduce the effect of a varying mass density across the substratesurface and thus reduce the variation in the depth and/or volume of themelt region 113. In general, the homogenizing layer 120 material isselected so that it will not melt during the subsequent annealingprocess and it can be selectively removed from the surface of thesubstrate after the annealing processes have been performed. In oneaspect, the homogenizing layer 120 is a material that is similar incomposition to the material that the features 101 are made from, suchas, for example, a polysilicon containing material. In another aspect,the homogenizing layer 120 is a silicon carbide containing material or ametal (e.g., titanium, titanium nitride, tantalum, tungsten).

Preferably, the thickness of the homogenizing layer 120 (e.g., d₁) isselected so that the heat capacity of the device structure is uniform.In one aspect, the thickness, d₁ of the homogenizing layer 120 isgoverned by:

d ₁=(α₁)^(0.5) ×[d ₂/((α₂)^(0.5))]

where

d₂=Thickness of the features 101 (see FIG. 5B)

α₁=κ₁/(ρ₁ C _(p1)) and

α₂=κ₂/(ρ₂ C _(p2))

where κ₁ equals the thermal conductivity of the material used to formthe homogenizing layer, ρ_(i) equals the mass density of the materialused to form the homogenizing layer 120, C_(p1) equals heat capacity ofthe material used to form the homogenizing layer 120, κ₂ equals thethermal conductivity of the material used to form the features 101, ρ₂equals the mass density of the material used to form the features 101,and C_(p2) equals the heat capacity of the material used to form thefeatures 101.

FIG. 6A Illustrates a series of method steps that may be used to formthe homogenizing layer 120 on a surface 102 of the substrate 100. Instep 190, shown in FIGS. 6A and 6B, the homogenizing layer 120 isdeposited over the surface 102 (e.g., features 101) of the substrate 100by use of a conventional deposition process, such as a chemical vapordeposition (CVD), plasma enhanced CVD, atomic layer deposition (ALD),plasma enhanced ALD, or spin coating type deposition process. In step192, shown in FIGS. 6A and 6C, the surface 102 of the substrate 100 thatcontains the homogenizing layer 120 is planarized using a chemicalmechanical polishing (CMP) process. In step 194, shown in FIGS. 6A and6D, the homogenizing layer is then selectively etched using a selectivematerial removal process, such as a wet etch or dry etch type processuntil a desired thickness d₁ is achieved. Next, an amount of incidentelectromagnetic energy can be delivered to the surface of the substratesurface to cause the uniform annealing/melting of the material containedin the melt regions 113.

Absorption Layer Over Homogenous Layer

FIG. 5C is a cross-sectional view of a substrate 100 that contains thedevice illustrated in FIG. 5B with an added layer 125 deposited thereonto adjust the optical properties of various regions on the surface ofthe substrate. In one aspect, the layer 125 is added to improve theabsorption of the electromagnetic energy 150 delivered to variousregions of the substrate 100. In one embodiment, the layer 125 is thesame as the coating 225 or the layer 226 described above. As shown inFIG. 5C the layer 125 is preferentially formed on the homogenizing layer120 to improve the selectivity of energy delivered to the siliconregions 112. The desired thickness of the layer 125 may vary as thewavelength of the delivered electromagnetic energy 150 varies.

Referring to FIGS. 6A-6G, in one embodiment, after performing steps 190through 194 the steps 196 and 198 may be used to form a selectivelydeposited absorbing layer 125. In step 196, shown in FIGS. 6E and 6F,the layer 125 is deposited over the features 101 and the homogenizinglayer 120 formed in steps 190-194, discussed above. In step 198, shownin FIGS. 6E and 6G, the layer 125 is removed from the top surface of thefeatures 101 by performing a material removal step, such as aplanarization process typically completed by use of a chemicalmechanical polishing (CMP) process. In one aspect, the deposited layer125 is used to alter the melting point contrast between one or moredesired regions on the substrate surface by allowing a differing amountof heat to be absorbed and transmitted to the melt regions 103 versusthe regions between the melt regions, which are not in direct contactwith the layer 125 and the homogenizing layer 120.

Diffraction Grating

One issue that arises when features of different sizes, shapes anddistances apart are exposed to electromagnetic radiation is thatdepending on the wavelength of the electromagnetic radiation the amountof energy applied to the features may experience constructive ordestructive interference due to diffraction effects that undesirablyvary the amount of energy, or energy density (e.g., Watts/m²), deliveredto a desired region. Referring to FIG. 7, the spacing of the features101 may differ such that the wavelength of the incident radiation variesacross the surface causing a variation in energy density deliveredacross the surface 102 of the substrate 100.

In one embodiment, as shown in FIG. 7, a layer 726 is grown to athickness that exceeds the height of all of features 101 to reduce thediffraction effect created by the irregular spacing between devices(e.g., features 101) formed on the surface of the substrate. In oneaspect, not shown, the surface 720 of the layer 726 is furtherplanarized (e.g., CMP process) to reduce any inherent topographicalvariation in the surface 720 of the substrate 10. In general, it isdesirable to reduce the topographical variation on the surface of thesubstrate to have a peak-to-valley variation (see “PV” in FIG. 7) acrossthe surface of the substrate of less than about a quarter of thewavelength (<¼λ) of the energy delivered during the annealing process.It is also desirable to have the average period between peaks (see “PP”in FIG. 7) across the surface of the substrate greater than about fivetimes the wavelength (e.g., >5λ) of the energy delivered during theannealing process. In one example, when using an 800 nm wavelength lasersource, it is desirable to reduce the inherent topographical variationin the surface 720 to an peak-to-valley variation of less than about 200nm and a period between peak variation greater than about 4000 nm. Inone aspect, the layer 726 is a carbon layer deposited by a CVDdeposition process or a material discussed in conjunction with layer125, coating 225, and layer 226 discussed above.

In one embodiment, the design of the devices formed on the surface of asubstrate that is exposed to incident electromagnetic radiation isspecifically designed and arranged so that a desired diffraction patternis created to improve the melting point contrast between differentzones. The physical arrangement of the various features are thustailored for a desired wavelength, or wavelengths, of the incidentradiation “B” (FIG. 7) used to anneal the surface of the substrate.

Forming Amorphous Region in a Substrate

In one embodiment, one or more processing steps are performed toselectively form an amorphous region 140 in an originally single crystalor polycrystalline material to reduce the amount of damage createdduring subsequent implantation processing steps and increase the meltingpoint contrast of the amorphous region 140 relative to other areas ofthe substrate. Implanting dopants in an amorphous region, such as anamorphous silicon layer will tend to homogenize the implantation depthof the desired dopant at a fixed ion energy, due to lack of densityvariation across the various planes found in crystalline latticestructures (e.g., single crystal silicon). The implantation in anamorphous layer will tend to reduce the crystalline damage commonlyfound in traditional implantation processes in crystalline structures.Therefore, when the amorphous region 140 is subsequently re-melted usingan anneal type process, as discussed above, the formed region can berecrystallized with a more homogenous doping profile and with reducednumber of defects. The re-melting process also removes any damagecreated from the implant process. The formation of the amorphous region140 will also reduced the melting point of the affected regions, whichcan thus improve the melting point contrast between the amorphous region140 and the adjacent single crystal regions 141.

In one embodiment, a short dose of energy (item “B” in FIG. 8) isdelivered to a substrate 10 to selectively modify and form an amorphoussilicon layer in a desired region (e.g., amorphous region 140). In oneaspect, a pulse, or dose, of electromagnetic energy is delivered to thedesired region for a sufficiently short period of time to cause rapidmelting and cooling of the affected amorphous region 140 to produce anamorphous region in the substrate. In this case the pulse of energy isfor such a short duration that it produce a high regrowth velocity inthe heated region to produce an amorphous region. In one aspect, there-growth velocity in the heated region is greater than about 12 m/sec.

In one aspect, a pulse of energy is delivered to a desired region of asilicon substrate for period of less than about 10⁻⁸ seconds. In thisaspect, the pulse of energy may be delivered from a laser that deliversa peak power greater than 10⁹ W/cm², and preferably in a range betweenabout 10⁹ and about 10¹⁰ W/cm² for a period of less than about 10⁻⁸seconds. In one aspect, the power, pulse duration, shape of thedelivered dose to create the amorphous silicon layer may be varied toachieve an amorphous region 140 of a desired size, shape and depth. Inone aspect, the wavelength of the delivered dose of energy is selectedor varied to achieve a desired melt profile. In one aspect, thewavelength may be in the UV or IR wavelengths. In one aspect, thewavelength of the laser may be less than about 800 nm. In anotheraspect, the wavelength may be about 532 nm or about 193 nm.

In one embodiment, a mask is used to preferentially form the amorphousareas in various regions of the substrate surface.

Electromagnetic Radiation Delivery

FIG. 9 is a cross-sectional view of a region of a processing chamberthat illustrates one embodiment in which an energy source 20 is adaptedto deliver an amount of energy to an anneal region 12 of the substrate10 from the backside surface 901 to preferentially melt certain desiredregions within the anneal region 12. In one aspect, one or more definedregions of the substrate, such as anneal region 12, are exposed to theradiation from the energy source 20 at any given time. In one aspect,multiple areas of the substrate 10 are sequentially exposed to a desiredamount of energy delivered through the backside surface 901 from theenergy source 20 to cause the preferential melting of desired regions ofthe substrate. In one aspect, the anneal region 12 is sized to match thesize of the die (e.g., item # 13 in FIG. 1), or semiconductor devices,that are formed on the top surface 902 of the substrate 10. In oneaspect, the boundary of the anneal region 12 is aligned and sized to fitwithin the “kurf” or “scribe” lines that define the boundary of eachdie. Therefore, the amount of process variation, due to the varyingamount of exposure to the energy from the energy source 20 is minimized,since any overlap between the sequentially placed anneal regions 12 canbe minimized. In one example, the anneal region 12 is a rectangularregion that is about 22 mm by about 33 mm in size.

In one embodiment, the substrate 10 is positioned in a substratesupporting region 911 formed on a substrate support 910 that has anopening 912 that allows the backside surface 901 of the substrate 10 toreceive energy delivered from the energy source 20. In thisconfiguration the radiation “B” emitted from the energy source 20 toheat regions 903 that are adapted to absorb a portion of the emittedenergy. The energy source 20 is generally adapted to deliverelectromagnetic energy to preferentially melt certain desired regions ofthe substrate surface. Typical sources of electromagnetic energyinclude, but are not limited to an optical radiation source (e.g.,laser), an electron beam source, an ion beam source, and/or a microwaveenergy source. In one aspect, the substrate 10 is exposed to a pulse ofenergy from a laser that emits radiation at one or more appropriatewavelengths for a desired period of time. In one aspect, pulse of energyfrom the energy source 20 is tailored so that the amount of energydelivered across the anneal region 12 and/or the amount of energydelivered over the period of the pulse is optimized to enhancepreferential melting of certain desired areas. In one aspect, thewavelength of the laser is tuned so that a significant portion of theradiation is absorbed by a silicon layer disposed on the substrate 10.For laser anneal process performed on a silicon containing substrate,the wavelength of the radiation is typically less than about 800 nm, andcan be delivered at deep ultraviolet (UV), infrared (IR) or otherdesirable wavelengths. In either case, the anneal process generallytakes place on a given region of the substrate for a relatively shorttime, such as on the order of about one second or less.

In one aspect, the wavelength of the emitted radiation from the energysource 20 is selected so that the bulk material from which the substrateis formed is more transparent to the incident radiation than the areasnear the top surface 902 that are to be preferentially melted by theexposure of the incident emitted radiation. In one aspect, the regionsthat are to be preferentially melted contain a material that absorbs anamount of the energy delivered through the backside of the substrate,such as a dopant material or ionizing crystal damage (e.g., crystaldefects, Frenkel defects, vacancies) created during the implantationprocess. In general the dopant materials may be boron, phosphorous, orother commonly used dopant material used in semiconductor processing. Inone embodiment, the bulk material from which the substrate is formed isa silicon containing material and the wavelength of the emittedradiation is greater than about 1 micrometer. In another aspect, theenergy source 20 contains a CO₂ laser that is adapted to emit principalwavelength bands centering around 9.4 and 10.6 micrometers. In yetanother aspect, the energy source 20 is adapted to deliver wavelengthsin the infrared region, which is generally between about 750 nm andabout 1 mm.

In one embodiment, an absorbing coating (not shown) is disposed over theanneal region 12 on the substrate 10 so that the incident radiationdelivered through the back of the substrate can be absorbed before itpasses through the substrate. In one aspect, the absorbing coating is ametal, such as titanium, titanium nitride, tantalum, or other suitablemetal material. In another aspect, the absorbing coating is a siliconcarbide material, amorphous carbon material, or other suitable materialthat is commonly used in semiconductor device manufacturing.

In one embodiment, two wavelengths of light are delivered to the desiredregions of the substrate, so that the first wavelength of light is usedto generate free carriers (e.g., electrons or holes) in the substratefrom dopants or other ionizing crystal damage found in the desiredannealing regions, so that the generated free carriers will absorb theenergy delivered through the back of the substrate at a secondwavelength. In one aspect, the first wavelength is the wavelength of“green light” (e.g., about 490 nm to about 570 nm) and/or shorterwavelengths. In one embodiment, the first wavelength is delivered at adesirable power density (W/cm²) to the desired region of the substratefrom a second source 920 that is on the opposite side of the substratefrom the energy source 20, shown in FIG. 9. In another embodiment, thetwo wavelengths (e.g., first and second wavelengths) are deliveredthrough the backside of the substrate from the source 20. In yet anotherembodiment, the two wavelengths (e.g., first and second wavelengths) atdesirable power densities (W/cm²) are delivered through the backside ofthe substrate from two separate sources of electromagnetic energy (notshown).

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. A method of thermally processing a substrate, comprising: positioningthe substrate on a substrate support comprising a heating element andincreasing the temperature of the substrate; delivering a first energyfrom a first energy source to the substrate; and delivering a secondenergy from a second energy source to the substrate, wherein the firstenergy or the second energy is annealing energy and the annealing energyis polarized laser energy.
 2. The method of claim 1, wherein the firstenergy source is a laser and the second energy source is a laser.
 3. Themethod of claim 2, wherein the first energy elevates the temperature ofthe substrate surface to a first temperature, and the second energybrings the temperature of the substrate surface to a second temperaturethat completes the thermal processing.
 4. The method of claim 1, whereinthe second energy source comprises a series of lasers.
 5. The method ofclaim 1, wherein an amount of the second energy is less than an amountof the first energy.
 6. The method of claim 1, wherein the first energyand the second energy are delivered to a first region of the substrate,the first region having an area less than a surface of the substrate. 7.The method of claim 1, wherein the first energy comprises a pulse ofenergy from the first energy source, and the second energy comprises apulse of energy from the second energy source.
 8. The method of claim 1,wherein the first energy and the second energy individually do not causea portion of the substrate to melt.
 9. A method of thermally processinga substrate, comprising: positioning the substrate on a substratesupport comprising a heating element and increasing the temperature ofthe substrate; delivering a pulse of first energy from a first energysource to the substrate; and delivering a pulse of second energy from asecond energy source to the substrate, wherein the first energy or thesecond energy is annealing energy and the annealing energy is polarizedlaser energy.
 10. The method of claim 9, wherein the first energy andthe second energy individually could not cause a portion of thesubstrate to melt.
 11. The method of claim 10, wherein the first energyand the second energy combined cause a portion of the substrate to melt.12. The method of claim 10, wherein the shape of the pulse of the firstenergy is varied as a function of time.
 13. The method of claim 12,where the shape of the pulse of the second energy is varied as afunction of time.
 14. The method of claim 13, wherein the first energysource and the second energy source are lasers.
 15. The method of claim9, wherein only the second energy is polarized.
 16. A method ofthermally processing a substrate, comprising: delivering a first energyfrom a first energy source to the substrate; and delivering a secondenergy from a second energy source to the substrate, wherein at leastone of the first energy and the second energy are polarized laserenergy, and wherein the first energy and the second energy individuallycould not cause a portion of the substrate to melt.
 17. The method ofclaim 16, wherein the first energy and the second energy combined causea portion of the substrate to melt.
 18. The method of claim 17, whereinboth the first energy and the second energy are polarized laser energy.